When a surgical operation is effected on the chest of a patient, an extracorporeal blood circulation circuit including an artificial lung is used in recent years in bypassing relation to the lung of the patient, and carbon dioxide is removed from the blood of the patient and fresh oxygen is added to the blood by the artificial lung.
The extracorporeal blood circulation circuit includes a blood reservoir for temporarily storing the blood s that air bubbles produced during the circulation of the blood will be removed from the blood, or for supplying stored blood to make up for a reduction in the rate of circulation of the blood. Blood reservoirs now in use in the art are roughly classified into a soft bag reservoir which is made of a soft material, and a hard shell reservoir which is made of a hard material. The soft bag reservoir is advantageous in that it has no blood-air interface, but disadvantageous in that it cannot hold a large amount of blood and cannot give an exact indication of how much blood is stored therein.
The hard shell reservoir can store a large amount of blood and allows the user to know the exact amount of blood stored therein. Other advantages of the hard shell container are that it can easily be united with an artificial lung, thus permitting an extracorporeal blood circulation circuit to be simplified, and also the blood can easily be debubblized when the extracorporeal blood circulation circuit is set up and primed. Japanese Laid-Open Patent Publication No. 59(1984)-57661, for example, proposes a hard shell blood reservoir combined with an artificial lung in view of the above functions and advantages.
It is very important that a hard shell blood reservoir be capable of reliably removing air bubbles which have been introduced into the blood through a blood extracting tube. If the blood containing air bubbles were returned to the patient, then the patient would suffer from the danger of embolism. The hard shell blood reservoir therefore has a debubblizer for removing air bubbles from the stored blood.
The applicant has devised a hard shell blood reservoir having a blood inlet port opening at a bottom thereof, as shown in FIG. 1 of the accompanying drawings. If a large amount of blood G flows from the blood inlet port 2 into the blood reservoir 4, the blood tends to be forcibly spouted as indicated by the dotted line 6 in FIG. 1. Therefore, the blood in the blood reservoir 4 is liable to be ununiform in flow, or air bubbles is apt to be trapped in the blood. The blood reservoir 4 has a blood debubblizer 8 for removing air bubbles from the blood. If the flow of the blood B becomes ununiform, then the debubblizing capability of debubblizer 8 is lowered, and also new air bubbles are produced by the ununiform blood flow.
One solution to the above problems due to the spouting of the blood B from the blood inlet port 2 into the blood reservoir 4 would be to provide a region for allowing the blood B to stay therein in the vicinity of the blood inlet port 2. However, if such a region is large enough to uniformize the blood flow caused by the spouted blood B, then the amount of blood stored in the blood reservoir 4 is increased, and hence the priming volume of the extracorporeal blood circulation circuit, with the result that the burden on the patent is also increased.